Prior glass bending systems such as, for example, the ones disclosed by U.S. Pat. Nos. 3,778,244, 4,202,681, 4,204,854, and 4,282,026 include bending apparatus having a holder positioned within a heating chamber above a roller conveyor to receive a heated glass sheet from the conveyor in preparation for bending. High quality glass can be achieved with this type of system if the conveyance is continued as the glass sheet is received by the holder from the conveyor since the glass sheet is then never stationary on the rollers in a manner that can result in roller marking of the lower glass surface. However, continued conveyance of the glass sheet as it is received by the holder necessarily results in sliding between the upper surface of the glass sheet and a downwardly facing surface of the holder. The surface material of the holder at which the sliding takes place must be capable of withstanding the sliding action and the heat involved without marking the upper surface of the glass sheet in its softened state. After the holder receives the heated glass sheet, a mold is moved under the holder and receives the heated glass sheet for bending. In certain applications, subsequent rapid cooling of the bent glass sheet provides tempering thereof to increase the glass strength and resistance to breakage.
Quite often, a pair of symmetrical right and left glass sheets are simultaneously bent such as in the manufacturing of right and left windows for vehicles. When a pair of sheets are bent on the type of system discussed above, it is conventional for one sheet to be conveyed forward of the other sheet in leading and trailing positions as the sheets are heated from room temperature to a sufficiently high temperature for bending. After the glass sheets have been conveyed for a sufficient distance to be heated to the required temperature, the longitudinal spacing therebetween along the direction of conveyance can change from the initial position due to slippage between the conveyor rollers and the glass sheets. Since the molds which receive the glass sheets from the holder are positioned in a fixed relationship with respect to each other, it is important for the glass sheets to be uniformly spaced with respect to each other and at the same location on the holder during each cycle in order to perform bending of both sheets to the desired shape. Repositioning of the glass sheets with respect to each other can be accomplished by holding one sheet as the conveyance of the other continues. However, such repositioning results in slippage between the sheet that is held and the rolls of the conveyor and can produce scratches on the lower roll supported glass surface.